Photo-optical pickoff for gyro

ABSTRACT

A photo-optical pickoff for a gyroscopic instrument to measure angular deflection between two movable parts which includes a variable resistance light responsive device mounted on one of the parts and activated by a light band, the movement of which is controlled by the other of the parts.

United States Patent Gleason et al.

[ Sept. 16, 1975 [54] PHOTO-OPTICAL PICKOFF FOR GYRO 3,205,718 9/1965 Wierenga et a1 74/5.6 A 3,439,170 4/1969 Zagone et a1. 74/5.6 A 1751 lnvemors= Dav'd Gleam; Ehnerd 3,457,794 7/1969 Parker 74/5.6 A Anderson, both Of Grand p x 3,489,017 1/1970 Parker 74/5.6 A MlCh- 3,522,993 8/1970 Gabriet 74/5.1 X

[73] Assignee: R. C. Allen, lnc., Grand Rapids,

Mich. Primary Examiner-Charles J. Myhre Assistant Examiner-William C. Anderson [22] Flled: 1973 Attorney, Agent, or FirmLockwood, Dewey, Zickert 21 Appl. 190.; 352,046 & Alex 52 U.S. c1. 74/5.6 A; 250/231 GY ABSTRACT [51] Int. Cl GOlc 19/28 A photo optical i k ff f a gyroscopic instrument to 1 1 held of Search 74/5-6 A, 5 R; 25O/211'K measure ang'ular deflection between two movable 250/231 GY parts which includes a variable resistance light responsive device mounted on one of the parts and activated [56] References Cited by a light band, the movement of which is controlled UNITED STATES PATENTS by the other of the parts.

2,512,598 6/1950 Barkalow 74/5.6 A 3,097.299 7/1963 Rasmussen 74/5.6 A x 17 Clams 12 Drawmg F'gures S a! 3,0 32 Q 25 4 I I8 .-z 2 v '1 1 55 24 5 mum-i BEP 1 SHEET 1 BF 3 PHOTO-OPTICAL PICKOFF FOR GYRO This invention relates in general to a gyroscopic instrument, and more particularly to a photo-optical pickoff for a gyroscopic instrument, and still more particularly to a photo-optical pickoff including a variable resistance light responsive device of infinite resolution.

The photo-optical pickoff of the invention is contactless. I-Ieretofore contactless pickoffs of the electromagnetic type have been well known. Such pickoffs are somewhat sensitive to temperature variation, must be powered by an alternating current, are sensitive to frequency harmonics produced between exitation voltage of the coils and the induced voltage of the gyro motor, are somewhat sensitive to electromagnetic radiation coming from the rotor motor. and are somewhat troubled by linearity. It has been also well known to provide optical pickoffs for gyros wherein a plurality of photocells or photovoltaic cells comprise the light responsive portion of the pickoff. Such optical pickoffs have not been entirely satisfactory inasmuch as they are sensitive to changes in light intensity and provide a step-type resistance change in the same manner as pickoffs using contact-type wire wound potentiometers.

The photo-optical pickoff of the present invention obviates the difficulties of heretofore known pickoffs in that it utilizes a variable resistance light responsive device in the form of a photo-potentiometer controlled by a very narrow light band. It should also be recognized the device effectively provides a variable output in an electrical circuit, and therefore may also be considered a variable output light responsive device. The photo-potentiometer may be in the form of a straight or curvate bar and the light band may be produced by a light pipe or carrier or by a shutter having a slit therein associated with a wide source of light energy. The pickoff may be used on any gyro-powered instrument and particularly on an instrument used in connection with the movement of vehicles, including ground vehicles and airborne vehicles. More specifically, the photo-optical pickoff is especially valuable with aircraft instruments of the gyro-powered type, including turn and bank, attitude, and directional indicators. It should be appreciated that the pickoff may be used on a single degree of freedom gyro or a two degree of freedom gyro. In either event, the pickoff would normally measure angular deflection between two movable parts, such as between the frame of a gyro and a gimbal pivotally mounted in the frame, or between two gimbals.

It is therefore an object of the present invention to provide a new and improved photo-optical pickoff for gyros capable of being operated by AC. or DC. potential and which is capable of producing better linearity throughout its range of operation than heretofore known electromagnetic pickoffs.

Another object of this invention is in the provision of a photo-optical pickoff and which provides greatly improved performance over heretofore known electromagnetic pickoffs in that it is less sensitive to temperature; it can operate directly from a DC. potential; it is not sensitive to frequency harmonics as is produced between the exitation voltage of the coils in an electromagnetic pickoff and the induced voltage in the gyro motor; it is not susceptible to electromagnetic radiation coming from the gyro motor, and'which is more simple and economical in construction.

A still further object of this invention is in the provision of a photo-optical pickoff for gyros which provides a greatly improved performance over heretofore known photo-optical pickoffs in that it is not sensitive to light intensity variation; it provides greater linearity in output, and it provides an output of infinite resolution rather than a stepped output as would be provided by a photo-optical pickoff utilizing the well known photocells or photovoltaic cells.

Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheets of drawings, wherein like reference numerals refer to like parts, in which:

FIG. 1 is a side elevational view of a gyroscopic instrument with parts broken away to show underlying parts and which utilizes the photo-optical pickoff according to the present invention;

FIG. 2 is a fragmentary top plan view of the gyro of FIG. 1 taken substantially along line 2-2 of FIG. 1;

FIG. 3 is a vertical elevational view and sectional view of a part of the photo-optical pickoff taken substantially along line 3-3 of FIG. 1;

FIG. 4 is a front elevational view of the variable resistance light responsive device of the photo-optical pickoff according to the present invention;

FIG. 5 is a top plan view of the device of FIG. 4;

FIG. 6 is a vertical sectional view taken substantially along line 66 of FIG. 4;

FIG. 7 is a perspective view of the light holder and lamp assembly shown in FIG. 1 for producing the band of light to control the light responsive device;

FIG. 8 is a greatly enlarged vertical sectional view taken substantially along line 8-8 of FIG. 7;

FIG. 9 is a front elevational view of a modified light responsive device according to the present invention differing only in that it is curvate instead of straight; FIG. 10 is an electrical schematic diagram of a typical circuit involving the pickoff according to the invention;

FIG. 11 shows a modified arrangement wherein the means of controlling the light band is accomplished by a shutter having a light-emitting slit therein; and

FIG. 12 is a diagrammatic view of a two degree of freedom gyro utilizing a pair of photo-optical pickoffs according to the invention.

The photo-optical pickoff of the invention is applicable for producing null output or linear output proportional to displacement. Inasmuch as a photo-optical pickoff is contactless and therefore frictionless, it is in this sense comparable to the well known electromagnetic contactless pickoff. The pickoff of the invention includes generally a photo-potentiometer which may be termed a variable resistance light responsive device having infinite resolution, and as can be appreciated, a resolution that is more infinite than that obtainable from a wire wound potentiometer. A light band defined by suitable means controls the output of the photo-potentiometer. Accordingly, it can be appreciated that relative deflection or motion between two movable parts in a gyroscopic instrument can be measured by the photo-optical pickoff of the invention wherein the photo-potentiometer is mounted on one of the parts and the light band producing means is mounted on the other of the parts The pickoff may be used on a rate gyro having a single degree of freedom, on a displacement gyro having two degrees of freedom, or any other type of gyro.

In a rate gyro used for aircraft navigation for measuring the rate of turn, a single degree of freedom gyro is employed wherein the gimbal is pivotally mounted on the frame and where the sensitive axis of the gyro is aligned with the axis about which rotational motion of the aircraft is to be measured. It should be understood that the sensitive axis here referred to is perpendicular to the gimbal pivot axis and the rotor spin axis. The pickoff then measures the relative movement between the gimbal and frame and specifically the angular deflection of the gimbal relative to the frame to translate the information into an electrical signal, the magnitude of which is proportional to rate of turn information. While preferably with respect to the photo-optical pickoff of the invention as applied to a rate of turn gyro the photo-potentiometer is mounted on the frame and the means for producing the light band is mounted on the gimbal, the location of these elements could be reversed. Moreover, as will become apparent hereinafter, the manner of producing the light band may take different forms.

Referring particularly to FIGS. 1 and 2, a rate gyro is illustrated for showing the photo-optical pickoff of the invention as applicable to one form of gyro although it should be appreciated that the photo-optical pickoff of the invention may be applied to any gyroscopic instrument where it is desired to measure the relative movement or motion between parts for obtaining a readout of the instrument. As is well known, the rate gyro is one having a single degree of freedom and the photo-optical pickoff of the invention may likewise be applied to gyros having two degrees of freedom. The rate gyro is generally designated by the numeral IS-and includes a frame 16 having opposed upstanding supports 17 and 18 which pivotally support a gimbal 19. Trunnion 20 extends from the support 17 to pivotally engage bearing 22 carried by the gimbal 19, while trunnion 21 extends from the gimbal to pivotally engage the bearing 23 carried by support 18. A suitably powered rotor assembly 24, which would include a motor and a rotor, is rotationally carried by the gimbal along a rotational axis perpendicular to the pivotal axis of the gimbal 19. It should be recognized that the rotor motor may be electrical or pneumatic where the rotor may therefore be electrically or pneumatically driven. A casing 25 encloses the gyro components. As can be appreciated, the sensitive axis of the gimbal would align with the particular axis of the vehicle about which motion is to be measured, whether it be yaw, pitch or roll motion.

The photo-optical pickoff of the invention is generally designated by the numeral and includes a variable resistance light responsive device in the form of a photo-potentiometer 31 mounted on the frame through the support 18 and means for producing a light band in the form of a lamp holder assembly 32 mounted on the gimbal 19. The photo-potentiometer 31 is connected in a suitable pickoff measuring circuit.

As seen particularly in FIGS. 4, 5 and 6, photo-potentiometer 31 includes a substrate 35 having an active face 36 on which is provided a thin metal film resistor 37, an electrode 38 insulated from the resistor 37, and a separating photosensitive portion 39. The photosensitive portion 39 may be made of a suitable photoconductive or photovoltaic material. Photoconductive materials defining a photo-resistor may be cadmium selenide, cadmium sulphide, or the like, all of which are conductive when subjected to light impingement, as represented by the light band 40 to connect the electrode 38 to the resistor 37 at the location of the light band. While the film resistor strip 37 is fixed, only a part of it is effectively in the pickoff measuring circuit depending on the position of the light band 40. The photo-potentiometer 31 may be of a type commercially available and which is made by Moririca Electronics, Ltd. of Yokohama, Japan, and available from Solar Systems, Inc. of Skokie, Illinois, or of any other suitable type.

Contact pads 41 and 42 at the opposite ends of the film resistor 37 are connected to the conductors 43 and 44'respectively, while contact pad 45 insulated from the other contact pads and the film resistor is connected to the electrode 38 and a conductor 46. Accordingly, conductors 43 and 44 are connected to the opposite ends of the film resistor 37, while conductor 46 is connected to the electrode 38, as can be also further understood by looking at the electrical schematic diagram in FIG. 10. It can be appreciated that the photo-potentiometer 31 is bar-shaped and straight so that the film resistor portion is elongated as well as the photosensitive portion and the output or resistance characteristic of the photo-potentiometer will depend upon the position of the light band 40 along the photo-potentiometer and in particular along the film resistor 37. The width of the photo-sensitive portion 39 along its length may be uniform as shown or variable. For example, certain desired characteristics may be obtained where the portion is of photovoltaic material to vary the output of the material depending on where along the length it is excited by light energy.

One form of pickoff measuring circuit in which the pickoff of the invention may be used is shown in FIG. 10. This circuit is one where excellent linearity is pro duced. However, any suitable circuit may be used. The input of the photo-potentiometer is applied to the conductors 43 and 44, as seen in FIG. 10, wherein a power supply 47 is connected across the film resistor, while the output of the photo-potentiometer is taken between the electrode 38 and the film resistor 37 The resistance of the film resistor 37 is approximately 10K ohms. A 10K ohm potentiometer 49 is connected in parallel to the film resistor 37 with the arm 50 of the potentiometer 49 being connected to one input of an impedance load 51. The other input of the impedance load 51 is connected to the electrode 38 of the photo-potentiometer, and the output terminal 52 of the impedance load may be suitably connected to further circuitry for obtaining the measurement of gimbal deflection. The impedance load 51 may take the form of an operational amplifier having relatively high impedance as it is preferable to have a high impedance on the output of the photo-potentiometer where precision linearity is required to measure deflection. Where only a null application is desired and the gyro is to be used as a nulling device, the impedance load may be either high or low. The photo-potentiometer may be energized with an alternating current or a direct current potential. Further,

the output of the photo-potentiometer may be varied in gain or gradient by varying the width of the light band 40.

The photo-potentiometer of the type commercially available from Solar Systems, Inc. has a permissible temperature range where the photosensitive material for the photo-resistor 39 is cadmium selenide of about to +50 C, and a peak spectral response is 7,000 i 200 A. It should be appreciated the photoresistor may be of other suitable materials which would have the same or different operating temperature and spectral response ranges. As seen particularly in FIGS. 2 and 3, the photo-potentiometer 31 is mounted on a bracket 54 that is in turn mounted on the frame support 18.

The lamp holder assembly 32, which produces the light band 40 to control the output of the photo-potentiometer, as seen most clearly in FIGS. 1, 2, 7 and 8, includes a lamp carrier or light pipe 58 which is formed of a suitable light transmitting material. Preferably, it is made of a clear plastic, such as Plexiglas material. The light carrier 58 may take any desirable shape, but it is illustrated as having an essentially square body, necked down at one end to define a rectangularly shaped face 59. The main body of the lamp carrier 58 includes a chamber 60 within which is positioned a subminiature lamp 61 of the incandescent, light-emitting diode or other suitable type for producing a source of light energy. Internally within the chamber 60 it is preferably painted or coated white to reflect the light of the lamp 61, while the exterior is preferably painted or coated black to prevent the escape of light except on the face 59. Similarly, it will be appreciated that the entry to the necked down portion from the chamber 60 would not be painted white to allow the light energy to pass into the necked down portion and out the face 59. Accordingly, the necked down portion essentially defines a light orifice for defining the light band 40. Preferably, the lamp 61, when of the incandescent type, includes a filament 62 that is aligned with the light orifice and therefore with the face 59 of the light carrier. As particularly seen in FIGS. 1 and 2, the lamp holder assembly is mounted on a bracket 65 which is in turn suitably secured to the gimbal 19.

It should be recognized that the photo-potentiometer may take some other shape where desired, such as a curvate shape shown by the photo-potentiometer 68 in FIG. 9. The arcuate extent may be of any angle or substantially circular. With this type of shape, linearity can be improved in a displacement gyro. The photo-potentiometer 68 includes a film resistor portion 69, an electrode 70 insulated therefrom, and a separating photosensitive portion 71. Electrode 70 is in the form of a bus bar having zero or very low resistance. Additionally, bus bars 72 and 73 are formed at the opposite ends of the film resistor portion 69 which would have essentially zero resistance and which would maintain electrical continuity in the overtravel range. Again, the photosensitive portion may be photoconductive or photovoltaic. A light band 74 would control the output of the photo-potentiometer.

The manner of defining a light band is shown in one form in the light carrier or pipe 32, but it will be appreciated that the light band could also be defined by means of a shutter having a slit formed therein and a diagrammatic showing of this form is illustrated in FIG. 11, wherein the photo-potentiometer 80 would have in opposed relation thereto, a light source 81 along its entire length and separated by a shutter 82 having a slit opening 83. More specifically, it can be appreciated that the light source 81 may take the form of an elongated light bar and a lamp and which would be mounted in fixed relation to the photo-potentiometer 80 and, for example, on the frame of a gyro. The shutter 82 would then be movably mounted or mounted on the gimbal and would take the form of a plate of opaque material with the slit opening so that light from the light source 81 would impinge on the photopotentiometer only through the slit opening at the position of the slit. While the photo-potentiometer is shown in straight bar form, it could be in curvate bar form as shown in FIG. 9.

It should be further appreciated as above mentioned that the photo-optical pickoff of the invention can also readily be applied to gyros having two degrees of freedom such as a displacement gyro and such is as diagrammatically illustrated in FIG. 12. This gyro includes a frame 90, a first gimbal 91 pivotally mounted on the frame, a second gimbal 92 pivotally mounted in the first gimbal 91 and along an axis perpendicular to the pivot axis of the first gimbal 91 and a rotor assembly rotationally mounted in the second gimbal 92 and having a spin axis 93 perpendicular to the pivot axis of the second gimbal and the pivot axis of the first gimbal. A first photo-optical pickoff 94 is mounted to measure motion between the frame and first gimbal 91 and a second photo-optical pickoff 95 is mounted to measure motion between the first gimbal 91 and the second gimbal 92. With respect to the pickoff elements which would include a photo-potentiometer and a light source, it can be appreciated, as heretofore suggested that they may be mounted on either of the two parts of the gyro between which relative motion is to be measured. Specifically, in connection with the first pickoff 94 the photo-potentiometer may be mounted either on the frame 90 or the first gimbal 91 and similarly the light source may be mounted either on the first gimbal 91 or the frame 90.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention, but it is understood that this application is to be limited only by the scope of the appended claims.

The invention" is hereby claimed as follows:

1. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a gimbal mounted on said frame for pivotal niovement about an axis, a rotor rotatably mounted on said gimbal about an axis normal to the pivot axis of said gimbal, and a photo-optical pickoff for measuring relative angular displacement between the frame and the gimbal, said pickoff comprising a first element mounted on the frame for movement therewith and asecond element coacting with the first element and, mounted on the gimbal for movement therewith, one of said elements being a variable resistance light responsive device having infinite and proportional resolution between the ends thereof and being insensitive to variation in light intensity, said light responsive device including a bar-shaped substrate, an elongated film resistor portion on one face of the substrate, a photosensitive portion adjacent the film resistor portion on said one face and of the same length thereof, an electrode portion on said one face adjacent the photosensitive portion insulated from the film resistor portion and of the same length thereof, and means for driving and loading said device, and the other of said elements being means defining a light band of narrow width coacting with the light responsive device for projecting onto and across the resistor, photosensitive and electrode portions of the light responsive device along the length and between the ends thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, and said resistor, photosensitive and electrode portions of said device being of such a length that the light band traverse along and between the ends of the portions will accord the maximum displacement between the frame and gimbal.

2. A gyroscopic instrument as defined in claim 1, wherein said photosensitive portion is of photoconductive material.

3. A gyroscopic instrument as defined in claim 1, wherein said photosensitive portion is of photovoltaic material.

4. A gyroscopic instrument as defined in claim 1, wherein said means defining a light band includes a light carrier having a light orifice, and a light source supplying light to said carrier.

5. A gyroscopic instrument as defined in claim 1, wherein said variable resistance light responsive device is said first element mounted on said frame, and said light band means is said second element mounted on said gimbal.

6. A gyroscopic instrument as defined in claim 1, wherein said light responsive device is connected to a source of electrical potential and includes a high impedance output.

7. A gyroscopic instrument as defined in claim 1, wherein said light responsive device is connected to a source of electrical potential and includes a low impedance output.

8. A gyroscopic instrument as defined in claim 1, wherein said driving and loading means includes a source of potential connected across said film resistor portion, and a high impedance load connected to the output of the device between the film resistor portion and the electrode.

9. A gyroscopic instrument as defined in claim 1, wherein the bar-shaped device is straight.

10. A gyroscopic instrument as defined in claim 1, wherein the bar-shaped device is curvate and coordinated with the relative angular movement between the frame and the gimbal.

11. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a first gimbal mounted on said frame for pivotal movement about an axis, a second gimbal pivotally mounted on the first gimbal for pivotal movement about an axis perpendicular to the pivot axis of the first gimbal, a rotor rotatably mounted on said second gimbal along an axis normal to the pivot axes of both said first and second gimbals, a first photo-optical pickofi' mounted on the frame and first gimbal for measuring relative angular displacement between the frame and first gimbal, a second photo-optical pickoff mounted on the first and second gimbals for measuring relative angular displacement between said first and same length thereof, an electrode portion on said one face adjacent the photosensitive portion insulated from the film resistor portion and of the same length thereof, and means for driving and loading said device, said means defining said light band coacting with said light responsive device for projecting onto and across the resistor, photosensitive and electrode portions of the light responsive device along the length and between the ends thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, and said resistor, photosensitive and electrode portions of said device being of such a length that the light band traverse along and between the ends of the portions will accord the maximum displacement between the frame and gimbal.

12. A gyroscopic instrument as defined in claim 11, wherein said bar-shaped variable resistance light responsive device is a photo-potentiometer.

13. A gyroscopic instrument as defined in claim 11, wherein said bar-shaped device is straight.

14. A gyroscopic instrument as defined in claim 1 1, wherein the bar-shaped device is curvate and coordinated with the relative angular movement between the gimbals and between the gimbal and frame.

15. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a gimbal mounted on said frame for pivotal movement about an axis, a rotor rotatably mounted on said gimbal about an axis normal to the pivot axis of said gimbal, and a photo-optical pickoff for measuring relative angular displacement between the frame and gimbal, said pickoff comprising a first element mounted on the frame for movement therewith and a second element coacting with the first element and mounted on the gimbal for movement therewith, one of said elements being a variable resistance light responsive device in the shape of a bar having infinite resolution between the ends thereof and being insensitive to variation in light intensity, and the other of said elements being means defining a light band of narrow width projecting onto and across the light responsive device between the ends and along the length thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, and said means defining a light band including a light carrier made of light transmitting material having a necked down portion terminating in a narrow and elongated rectangular face and an internal lamp receiving chamber, the chamber being coated with reflective material except at said necked down portion, the exterior of said carrier being coated with a material to prevent escape of light from the carrier except at said face, and a lamp mounted within said chamber for defining a light source.

16. A gyroscopic instrument as defined in claim 15, wherein said lamp includes a filament taking a rectilinear form as viewed from the end and being aligned with the rectangular face.

17. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a gimbal mounted on said frame for pivotal movement about an axis, a rotor rotatably mounted on said gimbal about an axis normal to the pivot axis of said gimbal, and a photo-optical pickoff for measuring relative angular displacement between the frame and the gimbal, said pickoff comprising a variable resistance light responsive device having infinite and proportional resolution between the ends thereof and being insensitive to variation in light intensity, said light responsive device being mounted on the said frame and including a bar-shaped substrate, an elongated film resistor portion on one face of the substrate, a photosensitive portion adjacent the film resistor portion on said one face and of the same length thereof, an electrode portion on said one face adjacent the photosensitive portion insulated from the film resistor portion and of the same length thereof, and means for driving and loading said device, and means defining a light band of narrow width coacting with the light responsive device for projecting onto and across the resistor, photosensitive and electrode portions of the light responsive device along the length and between the ends thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, said means defining a light band including a light carrier and a light source supplying light to said carrier both of which are mounted on said frame, and a shutter mounted on said gimbal and having a slit arranged adjacent the light carrier and ahead of the variable resistance light responsive device, and said resistor, photosensitive and electrode portions of said device being of such a length that the light band traverse along and between the ends of the portions will accord the maximum displacement between the frame and gimbal. 

1. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a gimbal mounted on said frame for pivotal movement about an axis, a rotor rotatably mounted on said gimbal about an axis normal to the pivot axis of said gimbal, and a photo-optical pickoff for measuring relative angular displacement between the frame and the gimbal, said pickoff comprising a first element mounted on the frame for movement therewith and a second element coacting with the first element and mounted on the gimbal for movement therewith, one of said elements being a variable resistance light responsive device having infinite and proportional resolution between the ends thereof and being insensitive to variation in light intensity, said light responsive device including a barshaped substrate, an elongated film resistor portion on one face of the substrate, a photosensitive portion adjacent the film resistor portion on said one face and of the same length thereof, an electrode portion on said one face adjacent the photosensitive portion insulated from the film resistor portion and of the same length thereof, and means for driving and loading said device, and the other of said elements being means defining a light band of narrow width coacting with the light responsive device for projecting onto and across the resistor, photosensitive and electrode portions of the light responsive device along the length and between the ends thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, and said resistor, photosensitive and electrode portions of said device being of such a length that the light band traverse along and between the ends of the portions will accord the maximum displacement between the frame and gimbal.
 2. A gyroscopic instrument as defined in claim 1, wherein said photosensitive portion is of photoconductive material.
 3. A gyroscopic instrument as defined in claim 1, wherein said photosensitive portion is of photovoltaic material.
 4. A gyroscopic instrument as defined in claim 1, wherein said means defining a light band includes a light carrier having a light orifice, and a light source supplying light to said carrier.
 5. A gyroscopic instrument as defined in claim 1, wherein said variable resistance light responsive device is said first element mounted on said frame, and said light band means is said second element mounted on said gimbal.
 6. A gyroscopic instrument as defined in claim 1, wherein said light responsive device is connected to a source of electrical potential and includes a high impedance output.
 7. A gyroscopic instrument as defined in claim 1, wherein said light responsive device is connected to a source of electrical potential and includes a low impedance output.
 8. A gyroscopic instrument as defined in claim 1, wherein said driving and loading means includes a source of potential connected across said film resistor portion, and a high impedance load connected to the output of the device between the film resistor portion and the electrode.
 9. A gyroscopic instrument as defined in claim 1, wherein the bar-shaped device is straight.
 10. A gyroscopic instrument as defined in claim 1, wherein the bar-shaPed device is curvate and coordinated with the relative angular movement between the frame and the gimbal.
 11. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a first gimbal mounted on said frame for pivotal movement about an axis, a second gimbal pivotally mounted on the first gimbal for pivotal movement about an axis perpendicular to the pivot axis of the first gimbal, a rotor rotatably mounted on said second gimbal along an axis normal to the pivot axes of both said first and second gimbals, a first photo-optical pickoff mounted on the frame and first gimbal for measuring relative angular displacement between the frame and first gimbal, a second photo-optical pickoff mounted on the first and second gimbals for measuring relative angular displacement between said first and second gimbals, each of said pickoffs including a variable resistance light responsive device and means defining a light band of narrow width, said light responsive device having infinite and proportional resolution between the ends thereof and including a bar-shaped substrate, an elongated film resistor portion on one face of the substrate, a photosensitive portion adjacent the film resistor portion on said one face and of the same length thereof, an electrode portion on said one face adjacent the photosensitive portion insulated from the film resistor portion and of the same length thereof, and means for driving and loading said device, said means defining said light band coacting with said light responsive device for projecting onto and across the resistor, photosensitive and electrode portions of the light responsive device along the length and between the ends thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, and said resistor, photosensitive and electrode portions of said device being of such a length that the light band traverse along and between the ends of the portions will accord the maximum displacement between the frame and gimbal.
 12. A gyroscopic instrument as defined in claim 11, wherein said bar-shaped variable resistance light responsive device is a photo-potentiometer.
 13. A gyroscopic instrument as defined in claim 11, wherein said bar-shaped device is straight.
 14. A gyroscopic instrument as defined in claim 11, wherein the bar-shaped device is curvate and coordinated with the relative angular movement between the gimbals and between the gimbal and frame.
 15. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a gimbal mounted on said frame for pivotal movement about an axis, a rotor rotatably mounted on said gimbal about an axis normal to the pivot axis of said gimbal, and a photo-optical pickoff for measuring relative angular displacement between the frame and gimbal, said pickoff comprising a first element mounted on the frame for movement therewith and a second element coacting with the first element and mounted on the gimbal for movement therewith, one of said elements being a variable resistance light responsive device in the shape of a bar having infinite resolution between the ends thereof and being insensitive to variation in light intensity, and the other of said elements being means defining a light band of narrow width projecting onto and across the light responsive device between the ends and along the length thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, and said means defining a light band including a light carrier made of light transmitting material having a necked down portion terminating in a narrow and elongated rectangular face and an internal lamp receiving chamber, the chamber being coated with reflective material except at said necked down portion, the extErior of said carrier being coated with a material to prevent escape of light from the carrier except at said face, and a lamp mounted within said chamber for defining a light source.
 16. A gyroscopic instrument as defined in claim 15, wherein said lamp includes a filament taking a rectilinear form as viewed from the end and being aligned with the rectangular face.
 17. A gyroscopic instrument for a vehicle comprising, a frame adapted to be mounted on the vehicle for movement therewith, a gimbal mounted on said frame for pivotal movement about an axis, a rotor rotatably mounted on said gimbal about an axis normal to the pivot axis of said gimbal, and a photo-optical pickoff for measuring relative angular displacement between the frame and the gimbal, said pickoff comprising a variable resistance light responsive device having infinite and proportional resolution between the ends thereof and being insensitive to variation in light intensity, said light responsive device being mounted on the said frame and including a bar-shaped substrate, an elongated film resistor portion on one face of the substrate, a photosensitive portion adjacent the film resistor portion on said one face and of the same length thereof, an electrode portion on said one face adjacent the photosensitive portion insulated from the film resistor portion and of the same length thereof, and means for driving and loading said device, and means defining a light band of narrow width coacting with the light responsive device for projecting onto and across the resistor, photosensitive and electrode portions of the light responsive device along the length and between the ends thereof in accordance with the relative angular displacement between the frame and gimbal to provide a resistance output directly proportional to the angular displacement, said means defining a light band including a light carrier and a light source supplying light to said carrier both of which are mounted on said frame, and a shutter mounted on said gimbal and having a slit arranged adjacent the light carrier and ahead of the variable resistance light responsive device, and said resistor, photosensitive and electrode portions of said device being of such a length that the light band traverse along and between the ends of the portions will accord the maximum displacement between the frame and gimbal. 